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OVERALL ABSTRACTIt is imperative that acetic acid is removed from a waste stream in the UREX+ process sothat nitric acid can be recycled and possible interference with downstream steps can be avoided.Acetic acid arises from acetohydroxamic acid (AHA), and is used to suppress plutonium in thefirst step of the UREX+ process. Later, it is hydrolyzed into hydroxyl amine nitrate and aceticacid. Many common separation technologies were examined, and solvent extraction wasdetermined to be the best choice under process conditions. Solvents already used in the UREX+process were then tested to determine if they would be sufficient for the removal of acetic acid.The tributyl phosphate (TBP)-dodecane diluent, used in both UREX and NPEX, was determinedto be a solvent system that gave sufficient distribution coefficients for acetic acid in addition to ahigh separation factor from nitric acid. This solvent system was tested under various TBPconcentrations in the dodecane to provide information that can be used for further flow sheetdevelopment. The role of water in the acetic acid removal step was quantified in this study andis reported here. The performance of the annual centrifugal contactor for this acetic acid removalstep was also quantified and reported here.Each step in the UREX+ process was examined to determine if there was any acetic acidinterference in the performance of any step of the UREX+ flow sheet that would make itnecessary to remove the acetic acid prior to that step. It was found that no interference withacetic acid was present. Therefore, the acetic acid removal step can be placed essentiallyanywhere in the process. For simplicity, it has been proposed to place the removal step at the endof the process after TALSPEAK where all desirable metals have already been extracted and thenitric acid waste stream is prepared to be recycled.iii